In radio communication systems such as 3GPP (Third Generation Partnership Project) WCDMA (Wideband Code Division Multiple Access), LTE (Long Term Evolution), and LTE-A (LTE-Advanced), and IEEE (The Institute of Electrical and Electronics engineers) Wireless LAN and WiMAX (Worldwide Interoperability for Microwave Access) communication systems, a base station (cell, transmit station, transmitter, eNodeB) and a terminal (mobile terminal, receive station, mobile station, receiver, UE (User Equipment)) each include a plurality of transmit/receive antennas, and employ MIMO (Multi Input Multi Output) technology to spatially multiplex data signals to realize high-speed data communication.
In these radio communication systems, in order to realize data communication between a base station and a terminal, it is necessary for the base station to perform various kinds of control for the terminal. To do this, the base station notifies the terminal of control information by using certain resources to perform data communication in the downlink and uplink. For example, the base station notifies the terminal of information on the allocation of resources, information on the modulation and coding of data signals, number-of-spatial-multiplexing-layers information on data signals, transmit power control information, and so forth to implement data signals. Transmission of such control information is realized using the method described in NPL 1.
Communication methods based on MIMO technology in the downlink are implemented using various methods such as a multi-user MIMO scheme in which the same resources are allocated to different terminals, and a CoMP (Cooperative Multipoint) scheme in which a plurality of base stations coordinate with each other to perform data communication.
FIG. 14 is a diagram illustrating an example in which the multi-user MIMO scheme is implemented. In FIG. 14, a base station 1401 performs data communication with a terminal 1402 via a downlink 1404, and performs data communication with a terminal 1403 via a downlink 1405. In this case, the terminal 1402 and the terminal 1403 perform multi-user MIMO-based data communication. The downlink 1404 and the downlink 1405 use the same resources in the frequency direction and the time direction. Further, the downlink 1404 and the downlink 1405 each control beams using a precoding technique and so forth to mutually maintain orthogonality or reduce co-channel interference. Accordingly, the base station 1401 can realize data communication with the terminal 1402 and the terminal 1403 using the same resources.
FIG. 15 is a diagram illustrating an example in which the CoMP scheme is implemented. In FIG. 15, the establishment of a radio communication system having a heterogeneous network configuration using a macro base station 1501 with a broad coverage and a RRH (Remote Radio Head) 1502 with a narrower coverage than this macro base station is illustrated. Now, consideration is given of the case where the coverage of the macro base station 1501 includes part or all of the coverage of the RRH 1502. In the example illustrated in FIG. 15, the macro base station 1501 and the RRH 1502 establish a heterogeneous network configuration, and coordinate with each other to perform data communication with a terminal 1504 via a downlink 1505 and a downlink 1506, respectively. The macro base station 1501 is connected to the RRH 1502 via a line 1503, and can transmit and receive a control signal and/or a data signal to and from the RRH 1502. The line 1503 may be implemented using a wired line such as a fiber optic line or a wireless line that is based on relay technology. In this case, the macro base station 1501 and the RRH 1502 use frequencies (resources) some or all of which are identical, thereby improving the total frequency utilization efficiency (transmission capacity) within a coverage area established by the macro base station 1501.
The terminal 1504 can perform single-cell communication with the macro base station 1501 or the RRH 1502 while located near the macro base station 1501 or the RRH 1502. While located near the edge (cell edge) of the coverage established by the RRH 1502, the terminal 1504 needs to take measures against co-channel interference from the macro base station 1501. There has been proposed a method for reducing or suppressing interference with the terminal 1504 in the cell-edge area by using the CoMP scheme in which neighboring base stations coordinate with each other for multi-cell communication (cooperative communication) between the macro base station 1501 and the RRH 1502. As the CoMP scheme, for example, the method described in NPL 2 has been proposed.